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A21
October 13, 2007 9:00 AM - 10:30 AM Room Room 302 |
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| Fentanyl vs Remifentanil for 4-10 Hour Cases — Simulations Based on Response Surface Models | |||||||||||||||||||||||||||||||||||
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Dhanesh K. Gupta, M.D., Sandeep C. Manyam, Ph.D., Kenward B. Johnson, M.D., Julia L. White, R.N., Talmage D. Egan, M.D. Anesthesiology & Neurological Surgery, Northwestern University Feinberg School of Medicine, Chicago, Illinois |
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INTRODUCTION: After intracranial and spinal procedures, neurologic examination facilitates monitoring of potentially devastating intraoperative and postoperative complications. With the increased use of transcranial motor evoked potentials, anesthetics must be conducted without muscle relaxants. Therefore, to minimize the potential for movement, higher anesthetic concentrations are required. We performed simulations of hypnotic-opioid anesthetics of various durations to determine the optimal target concentration pairs that would provide a 95% probability of no hemodynamic or movement response and provide the fastest awakening. METHODS: Response surface models describing the interaction between sevoflurane-remifentanil and propofol-remifentanil in preventing response to tetanic stimulation and to sedation (modified Observer's Assessment of Alertness/Sedation) based on volunteer data were generated and used to determine a variety of opioid/sedative combinations that produced clinically adequate anesthesia. Response surface models of sevoflurane-fentanyl and propofol-fentanyl were generated using a fentanyl:remifentanil potency ratio of 2.4:1. Published pharmacokinetic models were used to simulate dosing regimens that would maintain constant effect site concentrations to produce clinically adequate anesthesia, as determined by our response surface models, across the entire range of opioid-hypnotic combinations. These simulations were used to identify the opioid/sedative mixture that yielded the fastest recovery (OAA/S ≥4) from 0.5-10 hour anesthetics. RESULTS: The target concentration pairs that provided a 95% probability of no movement and no heart rate response to tetanic stimulation and an OAA/S ≤ 1 while producing the quickest return to an OAA/S ≥ 4 are shown in the table. DISCUSSION: These simulations demonstrate that targeting an anesthetic depth to avoid the need for neuromuscular blockade when using target controlled fentanyl infusions to provide the opioid component of either propofol or sevoflurane balanced anesthesia, will result in a very long time to emergence. Because of the pharmacokinetics of fentanyl, the optimal concentration pairs are weighted towards high concentrations of the hypnotic. These high concentrations of sevoflurane are known to decrease the motor and sensory evoked potential amplitudes. In contrast, because of the rapid elimination clearance of remifentanil, the optimal concentration pairs of remifentanil-sevoflurane avoid concentrations above 0.5 MAC. Therefore, remifentanil-hypnotic anesthetics are pharmacokinetically more favorable than fentanyl-hypnotic based anesthetics. In addition, the optimal concentration pairs of remifentanil-hypnotic that produce the most rapid awakening are favorable for evoked potential monitoring.[table1] Anesthesiology 2007; 107: A21 |
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